Welcome to YT and congrats on your new addition.
7 weeks is VERY young for a Yorkie pup to be placed in it's new home.
(Most reputable breeders agree that 12 weeks is the ideal age for placement.) Make sure that you are watching for signs of hypoglaucemia--the adjustment of her new home *may* stress her out and at such a small, young age, it it definately something to watch for.
I would recommend you continue her on the food she is accustomed to eating until she has adjusted to her new home. Then gradually swap her over to something else. In the meantime, research and determine which food you want to try to swap her over to. If you check the 'Health & Diet' section, there is a sticky with some of the more recommended brands of food (YT recommended anyway) and some of the companies will send you samples to try.
Good luck!